1. Field of the Invention
The present invention generally relates to an electromagnetic actuator for moving an object along a focusing direction and/or a tracking direction. Particularly, the object is directed to a lens holder.
2. Background Description
Generally, the operation of an information writing/reading apparatus is performed on a disk-shaped recording medium such as a compact disk, Magneto-Optical disk (MO) or the like.
However, a disk is usually not perfectly flat and symmetric. The disk usually contains inevitable warp and eccentricity. It causes misreading because the photo sensor of the optical head reads a laser reflected from the disk. If the disk has a warped surface or is eccentric, the laser would not be able to read correctly by the optical head. Therefore, the information writing and reading apparatus preferably includes means for moving the objective lens in response to the deviations resulting from the variable warped surface and/or the eccentricity of the disk. The movement is generally performed on a micro level along two orthogonal directions, for examples, a focusing direction perpendicular to the disk surface and a tracking direction parallel to the disk surface in order to compensate the focusing deviation and the tracking deviations respectively.
Further, for moving the objective lens in a micro level, there is a prior known objective lens drive unit described in the U.S. Pat. No. 5,659,525. FIGS. 1A and 1B shown the top view and cross section of the objective lens drive unit of the patent respectively. U.S. Pat. No. 5,659,525 to Akira Miyamae et al. discloses a lens holder 1 which is able to rotate along the tracking direction and movable along the focusing direction, around the shaft 7. The lens 2 is placed on the lens holder 1. The balancer 8 is opposite to the lens holder 2 according to the position of the shaft 7. Couples of focusing drive coils and the tracking drive coils are mounted to the lens holder 1 and the balancer 8. By the flux provided by the permanent magnet 6 and the electromagnetic attraction, the lens holder is therefore rotatable along the tracking direction and movable along the focusing direction. The outer yoke 9 is directed to provide placement for the permanent magnet 6. The inner yoke 10 is directed to limit the rotation range of the lens holder 1. A two dimensional restoring force is provided by the interaction of the magnetic piece 10 and the permanent magnet 6. In this case, once the tracking drive coil and the focusing drive coil are not actuated, the lens holder is able to return to a stationary neutral position.
Further referring to FIGS. 1C and 1D, a detailed structure of the magnetic piece 10 and the permanent magnet 6 is shown. The magnetic piece 10 is molded as an I shape. The permanent magnet 6 is curved with two polarization on one side. In this case, the construction is not easy to manufacture and takes time to complete. Moreover, the flux routes of the focusing drive coil 4 and the tracking drive coil 3 is not efficient.
It is therefore an object of the present invention to provide an electromagnetic actuator for obtaining micro movement along a focusing direction and micro rotation along a tracking direction.
According to a first aspect of the present invention, an electromagnetic actuator for moving an object along a focusing direction and a tracking direction includes a flux generator, having a first magnetic part and a second magnetic part, wherein the same polarization areas of the first magnetic part and the second magnetic part are opposite with a gap in order to generate a smooth first set of magnetic lines of force and a smooth second set of magnetic lines of force in an area of magnetic force; a first set of coils, connected to an object and positioned within the area of magnetic force, wherein the first set of coils moves the object along a direction of a shaft, especially in response to the tense of electric current actuated in the coils; a second set of coils, connected to the object and position around the area of magnetic force, wherein the second set of coils rotates the object around the shaft, in response to the tense of electric current actuated in the coils; and a metal piece, connected to the object and positioned adjacent to the first set of magnetic lines of force and the second set of magnetic lines of force in order to control the distance of the gap and further being able to provide a restoring force to return the object at a stationary neutral position when the coils are not actuated.
Preferably, the object is a lens holder for holding an objective lens of an information reading and writing optical head.
Preferably, the first set of coils is a focusing drive coil and the second set of coils is a tracking drive coil.
Preferably, a perpendicular line of the plane formed by the tracking drive coil is parallel to a tangent line of the cross circle of the shaft. Preferably, the flux generator is made by permanent magnets wherein the polarization areas of the permanent magnets are opposite within the gap.
Preferably, the electromagnetic actuator further includes another mirrored set of the flux generator, the first set of coils, the second set of coils and the metal piece.
According to a second aspect of the present invention, the electromagnetic actuator includes a flux generator, having a first magnetic part and a second magnetic part, wherein the same polarization areas of the first magnetic part and the second magnetic part are opposite with a gap in order to generate a smooth first set of magnetic lines of force and a smooth second set of magnetic lines of force in an area of magnetic force; a first set of coils, connected to an object and positioned within the area of magnetic force, wherein the first set of coils moves the object along a direction of a shaft, especially in response to the tense of electric current actuated in the coils; and a metal piece, connected to the object and positioned adjacent to the first set of magnetic lines of force and the second set of magnetic lines of force in order to control the distance of the gap and further being able to provide a restoring force to return the object at a stationary neutral position when the coils are not actuated.
According to a third aspect of the present invention, an electromagnetic actuator includes a flux generator, having a first magnetic part and a second magnetic part, wherein the same polarization areas of the first magnetic part and the second magnetic part are opposite with a gap in order to generate a smooth first set of magnetic lines of force and a smooth second set of magnetic lines of force in an area of magnetic force; a first set of coils, connected to the object and position around the area of magnetic force, wherein the second set of coils rotates the object around the shaft, in response to the tense of electric current actuated in the coils; and a metal piece, connected to the object and positioned adjacent to the first set of magnetic lines of force and the second set of magnetic lines of force in order to control the distance of the gap and further being able to provide a restoring force to return the object at a neutral central position when the coils are not actuated.